Taxi would be more than EUR 150-200 (one way) I think. This website suggests it could be up to EUR 260. Public transportations are good in the Netherlands but the park is out of town and 2 hours is long. Maybe taking a cab to the station on both ends (Amsterdam and 's-Hertogenbosch) and a train in-between could cut the time and be a good compromise. Renting a car could also make sense.
You can buy tickets for the Efteling online. I did it last year and did not have to wait at the entrance at all (but it's not like there was a long queue for regular tickets either). There are no express tickets to jump the queues for the rides as far as I know (the whole idea would seems at odd with the local culture and the atmosphere of the park in my opinion) but wait times for the rides are very reasonable (at least for the winter Efteling, summer might be a bit more crowded). There are special “luxury” tickets but they mostly offer lunch, souvenirs and entrance 30 min earlier, no special treatment in queues.
Don't expect Disneyland or Europa-Park, it's a completely different experience. They have started adding a few “thrill rides” to broaden their appeal (I highly recommend the “Villa Volta” madhouse but your kid is too young for that) but that's not the main focus. Signature attractions like the fairy tale forest don't even have queues at all, you just come along and wander around as you please.
About coming back late, in the winter it's getting dark early and it could be raining so I guess technically there is a somewhat higher risk of traffic accident but I don't see any reason to be concerned about safety.